Projection screens are used to display an image projected onto them. In a front projection screen, the image is viewed on the same side as the projector, and in a rear projection screen, the image is viewed on the opposite side of the screen as that of the projector. Projection screens use a diffusing mechanism, such as diffusing particles, to spread the projected image, to allow for viewing of the image from a wide variety of angles. The quality of the image, and angle from which it can be seen are important parameters for projection screens. The screen should also have physical integrity so a projected image is not distorted. Contrast ratio, gain, image definition, brightness, and screen uniformity are also important features of a projection screen.
A diffusing layer having spherical 2-15 micron, core-shell particles that are refractive index mismatched is described in U.S. Pat. No. 5,237,004.
U.S. Pat. No. 5,307,205 describes an article comprising a bi-layer sheet for use as a rear projection screen having 2-15 micron, core-shell particles. The diffusion layer faces the viewer.
A multi-layer structure for use with LED lighting is described in U.S. Pat. No. 6,878,436 produced from a co-extruded sheet having a diffusing layer and at least one substrate layer. The multi-layer extruded sheet has a very low contrast ratio and poor image quality.
When the diffusing layer is on the outside of a screen it is more likely to scratch, both during production and use. Scratches on diffusion screens in-use are so detrimental, that methods have been developed to remove or cover the scratches (i.e., as described in U.S. Pat. No. 5,170,287).
It was found that by placing the diffusing layer inside substrate layers, the overall performance of multi-layer screens (such as image definition, brightness, etc.) is not affected by the presence of superficial scratches or imperfections created during the handling of the screen, as it is typically observed in commercially available screen systems. The separation of the image-capturing layer from the sheet surface helps to preserve the image quality and prevent deterioration due to surface scratches. This reduced vulnerability to deteriorated image quality due to scratches also facilitates the overall fabrication and handling of projection screen systems. Additionally, it was found that multi-layer screens with an inner diffusing layer provide better image quality and an increased viewing angle when compared to screens having an outer diffusing layer. A further advantage is that the multi-layer screen of the invention is capable of being formed in a single co-extrusion process.